AO-40 Still Not Under Control

AO-40 Future Rests on Reducing Spin, Regaining Attitude Control

 

Artist's concept

NEWINGTON, CT, Feb 5, 2001--The key to a successful AO-40 recovery effort continues to be a matter of reducing the satellite's spin and regaining the ability to adjust its attitude from the ground. "The current problem is the lack of accurate AO-40 attitude data," AMSAT News Service said. Accurate data are not available because AO-40's sun sensor is not seeing the sun because of the satellite's attitude.

"Until accurate measurements can be made, AO-40 will remain in a semi-hibernation state," ANS said. Only when ground controllers can accurately determine the satellite's attitude will it be possible to change it and correctly aim AO-40's high-gain antennas for optimal reception on Earth--and that's assuming the transmitters are functioning on bands other than 2.4 GHz. Ground controllers have had no luck hearing AO-40's transmitters on the omnidirectional antennas on 2 meters, 70 cm or 1.2 GHz. Since the satellite's computer was reset and telemetry resumed December 25, the AO-40 ground team has been analyzing telemetry sent via the 2.4 GHz beacon--the only transmitter now operating.

In its latest dispatch on the next-generation Amateur Radio satellite, AMSAT-Germany recently waxed nearly poetic in describing AO-40's present situation.

"AO-40 is currently like a ship that's lying on a sandbar in the fog at low tide," an update on the AMSAT-DL Web site declared. Explaining the analogy, AMSAT-DL said AO-40 was "in the fog" because its high angle with respect to the sun temporarily prevents the sun sensors from providing attitude data. It's "at low tide" because the steep solar angle means less illumination of the solar panels and less energy produced. And it's "on a sandbar" because the satellite can't be set free from its present situation without some effort.

Ground controllers have been pinning their hopes on a previously announced "de-spinner" programming routine that would permit AO-40 spin control without having to rely on the sun sensors. The satellite's current spin rate is reported to be 17.7 RPM. But even if the programming fix fails, "it's no cause for panic," AMSAT-DL said. By April, controllers reason, the satellites sensors will again see the sun and "thanks to magnetorquing, spin and attitude can be actively improved upon the rising tide." Once the spin is reduced, sun angle improved, and antennas pointed, testing can resume. Still outstanding are tests of the VHF and UHF transmitters, the arc-jet motor, and the reaction wheels, among others.

Both AMSAT-DL President and AO-40 Project Leader Karl Meinzer, DJ4ZC, and AMSAT-NA President Robin Haighton, VE3FRH, have continued to be optimistic that AO-40 will have a useful life of Amateur Radio service. Command stations James Miller, G3RUH, Stacey Mills, W4SM, made a long-term prediction of AO-40's new orbit. They say that even after last year's incident--which silenced the satellite for nearly two weeks--and the resulting decrease of perigee, AO-40's orbit will be stable, although perigee will oscillate by several hundred kilometers.

AMSAT-DL says the recovery effort has been slowed somewhat because of limited access time on the part of the command team due to AO-40's current orbital parameters. "Whole Orbit Data collections are being utilized to recover telemetry data from orbital phases where AO-40 cannot be heard properly," AMSAT-DL reported. "The latest measurements show stable battery voltages and positive battery charging--except for eclipse times at perigee."

AMSAT News Service says Haighton and Meinzer have discussed progress being made in the recovery of AO-40. ANS says that if no commands were transmitted to the satellite it would take about three months before AO-40's attitude could be measured. The command team also was reported looking into the possibility of using a measurement of radiation falling on the solar cells to help determine AO-40's attitude. "If any of these attempts are successful, then adjustments to the satellite's attitude will begin earlier," ANS said.

Ground controllers consider the arc-jet motor "a critical item for making future orbit changes that will be required for satisfactory operation of the satellite," ANS said. The magnetorquing systems--needed for future attitude adjustments--also appear to be working, ANS said. There's no indication at this time that ground controllers plan to ever again fire the 400-newton propulsion system motor. It was during a test of the propulsion system that the satellite went silent in mid-December, precipitating the current situation.

Discussions of the future of AO-40 are expected to dominate the eighth AMSAT-DL Symposium on March 17 in Detmold, Germany, AMSAT-DL said.

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